Of carboxylate anions

Ba.sic Hydrolysis. Throughout most of history, soap was manufactured by boiling an ester with aqueous alkaU. In this reaction, known as saponification, the ester is hydroly2ed with a stoichiometric amount of alkaU. The irreversible formation of carboxylate anion drives the reaction to completion. 

Finally a proton transfer leads to formation of carboxylate anion 3. Of particular interest is the benzilic acid rearrangement of cyclic diketones such as 4, since it... 

Two methods for converting carboxylic acids to esters fall into the mechanistic group under discussion the reaction of carboxylic acids with diazo compounds, especially diazomethane and alkylation of carboxylate anions by halides or sulfonates. The esterification of carboxylic acids with diazomethane is a very fast and clean reaction.41 The alkylating agent is the extremely reactive methyldiazonium ion, which is generated by proton transfer from the carboxylic acid to diazomethane. The collapse of the resulting ion pair with loss of nitrogen is extremely rapid. 

Especially for large-scale work, esters may be more safely and efficiently prepared by reaction of carboxylate salts with alkyl halides or tosylates. Carboxylate anions are not very reactive nucleophiles so the best results are obtained in polar aprotic solvents45 or with crown ether catalysts.46 The reactivity order for carboxylate salts is Na+ < K+ < Rb+ < Cs+. Cesium carboxylates are especially useful in polar aprotic solvents. The enhanced reactivity of the cesium salts is due to both high solubility and minimal ion pairing with the anion 47 Acetone is a good solvent for reaction of carboxylate anions with alkyl iodides48 Cesium fluoride in DMF is another useful... 

Since the inception of our work Jere, Miller and Jackson have published kinetic and stereochemical data on the hydrogenation of alanine (19). Important in their analysis is the observation that amino acids must be in their protonated form to undergo facile hydrogenation since reduction of carboxylate anions is significantly more endothermic than protonated acids (19). Control of pH is important for two reasons at neutral pH amino acids exist as zwitterions and the resultant hydrogenation products are basic. For these reasons a full equivalent of phosphoric acid (or similar acid) is required to obtain high yields. 

Radicals, (34), that subsequently dimerise, are also obtained through the anodic oxidation of carboxylate anions, RCO20, in the Kolbe electrolytic synthesis of hydrocarbons ... 

Anodic decarboxylation proceeds via a C—C bond scission of carboxylate anions to afford the Kolbe dimer,197 i.e.,... 

The decarboxylation of carboxylate anions is carried out chemically by a variety of one-electron oxidants such as lead tetraacetate, uranyl nitrate, peroxides, quinones, pyridinium cations, etc.199 Importantly, the carboxylate anion (as... 

The trapping of allyl radicals with other open-shell species can be studied in all reactions in which a sufficiently high concentration of radicals is created and in which the concentration of nonradical trapping agents is low. This prerequisite has been met in Kolbe electrolysis reactions, in which radicals are generated by one-electron oxidation of carboxylate anions. One of the simplest systems, the reaction of methyl radicals with... 

The presence of carboxylic anion may be identified by the following two tests ... 

The corrosion process can be inhibited by the addition of phosphate or polyphosphate ions [344], inorganic inhibitors as, for example, chromate ions [336], adsorbed alcohols [345], adsorbed amines, competing with anions for adsorption sites [339,] as well as saturated linear aliphatic mono-carboxylate anions, CH3(CH2)n-2COO , n = 7 — 11, [24]. In the latter case, the formation of the passive layer requires Pb oxidation to Pb + by dissolved oxygen and then precipitation of hardly soluble lead carboxylate on the metal surface. The corrosion protection can also be related to the hydrophobic character of carboxylate anions, which reduce the wetting of the metal surface. 

Since the equilibrium constant for binding of EtO to the crown complexed Ba and Sr + ions is >10" m in both cases [9,28], the affinity of carboxylate anion for the ligated metal ions turns out to be large enough (K3> 10 m ) to ensure a virtually complete anchorage to the metal in the dilute solutions of the catalytic experiments. 

If these anions are oxidized at carbon anodes instead of Pt anodes, the main product is not the Kolbe dimer but an ester of the original carboxylic acid. This reaction (Hofer-Moest) is explained by the inherent instability of C radicals at highly anodic potentials, which are necessary for the anodic oxidation of carboxylate anions. At these potentials, the C radicals are oxidized to carbonium ions that react with carboxylate anions forming esters ... 

Thermodynamically, the latter reaction is to be expected, as C radicals exhibit an oxidation potential that is at least 1 V more negative than the oxidation potential of carboxylate anions (213, 214). 

Simple alkylations of carboxylate anions, by such alkylating agents as alkyl halides, dialkyl sulphates, and quaternary ammonium compounds, are generally straightforward SN2 reactions, and will not be discussed here. 

Typical synthetic procedures include the reaction of alkyl halides with the silver salts of carboxylic acids, the reaction of carboxylate anions in alkali with an excess of a dialkyl sulphate, (especially dimethyl sulphate), and heating tertiary184 or quaternary ammonium salts of carboxylic acids. These routes are particularly valuable for the preparation of esters of seriously sterically hindered acids. For example, Fuson et al.iK made the methyl ester of 2,4,6-triethylbenzoic acid by heating the tetramethyl ammonium salt to 200-250°C, viz. 

It was proposed that propagation proceeds by reaction of carboxyl anion with epoxide to form an ester-alkoxide anion which can react in turn with anhydride to form ester and another carboxyl anion. The rate-determining step was thought to be the reaction of carboxyl anion with epoxide, which would lead to first-order kinetics with respect to epoxide concentration. 

Protonation of the amino group usually induces a shielding of all carbon atoms, explained in terms of electric field effects [84] and CH bond polarizations [338], and follows the pattern observed on protonation of carboxylate anions (Section 4.7.4). 

Other synthetically useful additions of carboxylate anions to ir-allylpalladium complexes have been demonstrated, as illustrated in equations (52-54).175-179 Harder oxygen nucleophiles, such as phenox-ides175,176 and alkoxides,175-180 can also be added to ir-allylpalladium complexes (equation 55). Finally, the addition of NO2 to allylpalladium chloride dimer results in the production of ally nitrite (equation 56).18 ... 

This value shows that the rate of the reaction between alkoxide anion and anhydride (Eq. (18)) is about five times higher than that of the reaction of carboxylate anion with epoxide (Eq. (19)). Since it holds for the stationary state of copolymerization ... 

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